Evaporative emission regulations for vehicles require the control of polluting substances (primarily hydrocarbons) from the vehicle as the vehicle sits unused. Evaporative emissions can leak out of a vehicle from many sources including the air intake system, fuel tank, and exhaust gas recirculation (EGR) system. In the past, only the evaporative emissions from the fuel tank and fuel delivery system were captured, such as with carbon-filled canisters. However, with increasing emission regulations it has become necessary to expand evaporative emission capture technology to other vehicle components such as the air intake system.
It has been found that a significant amount of volatile hydrocarbons from several sources collect in the air intake system of the automobile engine after the engine has been shut off. These hydrocarbons are then discharged into the atmosphere after the engine has been shut off. Prior art systems and methods devote relatively little attention to prevention of the emissions of such hydrocarbons through the air induction system of the engine since the amounts of such emissions are relatively small as compared to the emissions of hydrocarbons from the fuel system and the exhaust gas stream which would pass into the atmosphere if left untreated. Nevertheless, in view of the increasingly stringent federal and state regulations mandating the elimination of all emissions of uncombusted hydrocarbons in the atmosphere to the extent technically feasible, it is desirable to provide equipment to adsorb such hydrocarbons.
A significant portion of a vehicles evaporative emissions are emitted from the air intake system during the vehicles off-cycle as a result of fuel injector leakage, residual fuel puddle evaporation, and blow-by gas from the PVC system. These substances need to be retained within the air intake system until the powertrain is again used when the retention system will give up the harmful substances to be consumed and controlled through the normal exhaust emission control systems.
There are several ways to control the outward flow of pollutants from the air intake system of an automobile. One such technique is the careful shaping of the ducting and filter box. However, this method is often not sufficient to meet the regulatory requirements. Accordingly, other methods must be used such as the incorporation of systems in the air intake system that use some form of carbon to absorb the pollutants during the rest cycle. When the vehicle is next started, the in-rushing air will draw the pollutants from the adsorbent and deal with them through the normal exhaust system pollution controls. This inward air rush also regenerates the adsorption systems so that they may be reused. Unfortunately, these extra adsorption systems add cost, weight and complexity to a vehicle and often restrict the air flow.
In additional efforts to reduce inadvertent evaporative emissions from the air intake system, many types of filters have been developed. Examples of filters for use in the intake system of a vehicle are found in U.S. Pat. No. 6,432,179 to Lobovsky et al. and U.S. Patent Application Publication No. U.S. 2002/0029693 to Sakakibara et al., both of which are incorporated herein by reference. The publication of Sakakibara et al. discloses several embodiments of hydrocarbon adsorbing devices having a case surrounding an inner cylinder portion. A hydrocarbon adsorbent material is provided in a chamber defined by the case and the inner cylinder portion. The inner cylinder portion has a central bore that extends through its length to permit induction air to pass therethrough, and also has windows that allow any hydrocarbons in the induction system to pass through a filter surrounding the inner cylinder portion to the hydrocarbon adsorbent material in the chamber to be adsorbed thereby.
U.S. patent application Publication Ser. No. US 2002/0043156 A1 discloses a housing securing an air filter having an air stream inlet and an air stream outlet. The air filter comprises a filter media disposed on a support that is disposed within, or secured to, the housing and an air permeable hydrocarbon adsorbing material is disposed between the filter media and the support at the air stream outlet end of the filter. According to the publication, the hydrocarbon adsorbent can be any suitable hydrocarbon adsorbing material. However, only activated carbon cloth, woven carbon fibers and a spun bound material impregnated with carbon powder or containing carbon granules, are exemplified.
EP 1 110 593 A1 is similar to the U.S. patent application Publication discussed above. The EP Patent Application discloses an air filter assembly including a housing and a plurality of filter layers disposed in the housing. One of the filter layers is a carbon impregnated polyurethane foam layer to remove hydrocarbon vapors diffusing through an air inlet to the filter when the engine is shut-off.
Furthermore, systems and methods for adsorbing uncombusted hydrocarbons in the exhaust gas stream of an automobile are also well known. These systems and methods are particularly useful for adsorbing uncombusted hydrocarbons emitted during the cold start of the automobile engine.
For example, U.S. Pat. No. 4,985,210 is directed to an exhaust gas purifying apparatus for an automobile employing a three-way catalyst with either a Y-type zeolite or a mordenite used in a hydrocarbon trap upstream of the three-way catalyst. In the embodiment of FIG. 2 of U.S. Pat. No. 4,985,210, a bed of activated carbon is disposed upstream of an adsorbent zone. A solenoid-operated valve mechanism serves to direct the exhaust gas stream either through or around the activated carbon bed, depending on the temperature of the exhaust gas stream, and then through the adsorbent zone and the three-way catalyst.
U.S. Pat. No. 5,051,244 is directed to a process for treating an engine exhaust gas stream in which the gas stream is directed through a molecular sieve in an adsorbent zone during the cold-start phase of engine operation. When the hydrocarbons begin to desorb, the adsorbent zone is by-passed until the catalyst is at its operating temperature, at which point the gas stream is again flowed through the adsorbent zone to desorb hydrocarbons and carry them to the catalyst zone. A paper by M. Heimrich, L. Smith and J. Kotowski entitled Cold-Start Hydrocarbon Collection for Advanced Exhaust Emission Control, SAE Publication Number 920847, discloses an apparatus which functions in a manner similar to that of U.S. Pat. No. 5,051,244.
U.S. Pat. No. 5,125,231 discloses an engine exhaust system for reducing hydrocarbon emissions, including the use of beta zeolites as hydrocarbon adsorbents. Zeolites having a silica/alumina ratio in the range of 70/1 to 200/1 are preferred adsorbents. The apparatus includes by-pass lines and valves to direct exhaust gases from a first converter directly to a second converter during cold-start operation and when the first converter reaches its light-off temperature, to either by-pass the second converter or recycle effluent from it to the first converter.
U.S. Pat. No. 5,158,753 discloses an exhaust gas purifying device comprising: a catalyst device installed in the exhaust gas path of an internal combustion engine for treating the exhaust gas of the engine; an adsorbing device installed in the exhaust gas path between the catalyst device and the internal combustion engine, for treating the exhaust gas of the engine. One embodiment includes a heat exchanger for performing heat transfer between the exhaust gas flowing from the internal combustion engine to the adsorbing device and the exhaust gas flowing from the adsorbing device to the catalyst device. Alternatively, the catalyst device includes a catalyst secured in the low-temperature-side gas flow path of a heat exchanger, and the exhaust gas flowing from the internal combustion engine to the adsorbing device is allowed to flow to the high-temperature-side gas flow path of the heat exchanger.
U.S. Pat. No. 6,171,556 discloses a method and apparatus for treating an exhaust gas stream containing hydrocarbons and other pollutants. The method comprises the steps of flowing the exhaust gas stream through a catalytic member comprising a monolith body having a first catalyst zone and a second catalyst zone therein to contact a catalyst in a first catalyst zone to convert at least some of the pollutants in the exhaust gas stream into innocuous products. The exhaust gas stream is then discharged from the catalytic member and flowed through an adsorbent zone to adsorb at least some of the hydrocarbon pollutants with an adsorbent composition. The exhaust gas stream is discharged from the adsorbent zone and flowed to the second catalyst zone to convert at least some of the pollutants into innocuous products. The exhaust gas stream, so treated, is then discharged to the atmosphere through suitable discharge means. A preferred adsorbent is a zeolite, having a relatively high silica to alumina ratio and a low relative Bronsted acidity. The preferred adsorbent compositions comprise beta zeolites.
As discussed above, zeolites are often used as coatings on monolithic substrates for various high temperature adsorption and catalytic applications. In these cases, inorganic binder systems are used that survive exposure to high temperatures (e.g., >500° C.) and provide good coating adhesion. However, for low temperature application (e.g., <500° C.), inorganic type binders are often not suitable since their binding characteristics are severely diminished. In these low temperature applications, organic polymer binders are ideal since they are structurally stable and provide excellent coating adhesion. This is accomplished by the addition of suitable stabilizing agents to the slurry formulation.
For example, commonly assigned U.S. Patent Publication No. 2004/0226440 (published Nov. 18, 2004) discloses a hydrocarbon adsorption unit. The unit is positioned in the air intake system and has an air intake and air outlet. According to the application the adsorber material may be silica gel, a molecular sieve and/or activated carbon and contains an organic polymer binder, as well as an anionic, nonionic or cationic dispersant, that will cause the material to adhere to the surface of a substrate.
Without proper choice of these stabilizing agents, interparticle agglomeration of zeolite particles or coagulation of zeolite and binder particles will occur, thus rendering the slurry unstable for coating application. As a result, a zeolite-based coating formulation must be developed that not only has good adhesion (particularly to metal substrates) at low temperature, but also excellent adsorption characteristics.
As previously mentioned, a major challenge for creating a hydrocarbon adsorber for the air intake system is to minimize the impact of the hydrocarbon adsorber on the air intake restriction. A further challenge is to create a hydrocarbon adsorber that adds little cost to the system, keeps restriction low, and provides sufficient hydrocarbon adsorption capacity for the particular application.
One possible way to do accomplish these objective is disclosed in U.S. Patent Publication No. 2002/0043156, incorporated herein by reference. The '156 publication discloses an integrated air filter and hydrocarbon adsorbing apparatus comprising a filter media disposed in a screen support and an air permeable hydrocarbon adsorbing material disposed between the filter media and the screen support. The '156 publication also discloses, in an alternative embodiment, an integrated air filter and hydrocarbon adsorbing apparatus comprising a hydrocarbon adsorbing coating which is directly disposed on a portion of the air filter. The '156 publication generally discloses the use of any suitable hydrocarbon adsorbing material, however, only exemplifies carbon cloth, carbon fibers, carbon powder, and carbon granules. Furthermore, the '156 publication does not discuss any specific requirements for the use of a coating slurry.
Accordingly, it is the object of this invention to provide a hydrocarbon adsorbent within the air intake system of a motor vehicle for adsorbing volatile hydrocarbons emitted after the engine has been shut-off, and thereby reduce or prevent the emission of such hydrocarbons into the atmosphere.